The quasi-steady-state (QSS) method essentially approximates the mid-term and long-term dynamic simulations by assuming that the short-term dynamics are infinitely fast leading to computation of a sequence of equilibrium points. The advantage is that the method is fast while the accuracy is acceptable. Modeling issues relative to mid-term voltage stability assessment in the time domain are explained. Appropriate models of the synchronous generator, the armature current limiter and the under load tap changer are provided. The QSS method can be further extended to include a singular value analysis. The resulting singular vector provides insight into voltage collapse prevention strategies. Test results are shown on WSCC reduced system.